DESCRIPTION: Treatment for obesity has proven difficult as most reduced obese individuals regain the weight which had been lost. The lack of success in treating obesity argues for strategies to prevent obesity or weight re-gain. The PIs propose to use 3 clinically appropriate levels of fat intake in a population at-risk for weight gain in a long-term study where energy intake and macronutrient composition is verified by multi-method techniques. Primary Aim-Prevention of weight gain. The PI will determine the effects of 3 levels of verified dietary fat intake on body weight and body composition in college students at-risk for weight gain. We hypothesize that ad libitum diets which contain greater than 35 percent fat will promote weight gain compared to subjects who ingest ad libitum diets which contain 28 to 32 percent fat or 25 percent fat or less. Specifically, the PI expects a dose response for the level of fat in the diet for body weight and fat mass. Secondary aims will may contribute to our understanding of how various levels of fat intake may prevent or promote obesity and may provide explanation for the anticipated differences in individual responses with the groups. Association of fat intake to total energy intake. The PI expects that subjects consuming diets with higher amounts of fat to have greater total energy intakes and will therefore show weight gain in a dose response fashion. Specifically, the PI will hypothesize that subjects consuming ad libitum diets with 35 percent fat or greater will show an increase in total energy intake compared to subjects consuming a 28 to 32 percent fat diet or subjects consuming a diet of 25 percent fat or less. Individual response - the PI expects subjects with greater body fat to gain more weight and fat mass compared to leaner subjects and expect subjects who are restrained eaters to gain less weight than those who exhibit disinhibited eating. Although the PI expects increase energy intake for the groups that receive high fat intakes, they do not expect all subjects within each group to respond in similar fashion. The long-term results expect to show those subjects who gained the least amount of weight during the intervention will have the lowest weights 1,2 and 3 years post intervention. The results of this study should advance our understanding of the role of dietary fat in the prevention of obesity and weight re-gain.